By any standard, nonrationality is an undertheorized concept in sociology. This paper attempts to open a discussion on nonrationality by analyzing one of the most fruitful theorizations of the concept: Simmel's. Simmel developed a theory that placed nonrationality on the same plane with rationality and attributed to the former a role as fundamental as the latter's in the foundations of action, and as central as the latter's in the generation of existential meanings. The gradual eclipse of the nonrational elements of life in the expanses of a modern, highly rationalized world imply, then, an impoverishment of being. I argue that Simmel's theory of the nonrational can serve as a model capable of enriching our understanding of society and of the person and can, in this sense, serve as a counterpoint to current sociological theories that emphasize the rational elements of life and conceive the person in primarily rational terms